This should then allow to redirect ports. So if you need to proxy existing apache via nginx or lighttpd and you do not want to switch apaches' default port 80, then the below rules will do the appropriate redirection to port 81 where nginx/lighttpd server is listening, serving static content and proxying to apache for dynamic content:

If you are switching out static content that have gotten cached in nginx, the head of the cached files usually stores the file path that can be greped for and the file removed. One you hit the url again, it will recreate the new cached file at the same location.